This invention relates to a tone signal generating device which can be used in an electronic musical instrument, or in other tone generating or synthesizing instruments, and more particularly to the device which can be simplified in circuitry required for various operations for tone signal generation.
Many kinds of operations are performed for generating a tone signal. Among them are, for example, a phase address signal operation for tone waveform generation, an envelope waveform signal generation operation, an amplitude level scaling operation with respect to a tone waveform signal, and a tone waveform interpolation operation. Such operations have conventionally been performed by individual dedicated operation circuits. Also some of the above mentioned operations involve further operations for scaling coefficients or accumulating data, which have also been performed by individual dedicated operation circuits, coefficient scaling multipliers and accumulators. For example, Japanese patent laid-open publication No. Sho 63-125990 (corresponding to U. S. Pat. No. 4,928,569) discloses an envelope waveform generating device in which various operations are performed by individual dedicated circuits.
As another example, Japanese patent laid-open publication No. Hei 1-101599 discloses the feature of using a common operation circuitry on time divisional basis for performing an operation for scaling the amplitude of a tone waveform signal by an interpolation coefficient used in interpolation operation of a tone waveform sample value along with an operation for scaling the amplitude of a tone waveform signal by an envelope coefficient.
However, there arises a problem that the number of required operation circuits and the size of overall circuitry tend to increase, if various operations for tone signal generation are performed by individual dedicated operation circuits as in the prior art.
Further, in the prior art where operations for scaling the amplitude of a tone waveform signal by an interpolation coefficient and by an envelope coefficient are performed in a common circuitry, circuitry reduction can be attained only in an extremely slight degree. Sharing an operation circuitry for operations of similar characteristics as mentioned can only provide an extremely limited level of circuitry reduction.